Electronic control system for internal combustion engine

ABSTRACT

Fuel injectors for an internal-combustion engine are controlled by duration-modulated pulses whose width depends on a plurality of parameters, namely the rotational speed and the temperature of the engine and the air pressure at two points of the intake manifold. The width of the modulated pulses depends on the magnitude of one parameter and on binomials of the other parameters. A computer formed by cascaded operational amplifiers with fractional gain and adding circuits establishes the variable operating period of the injectors which are provided with two coils, i.e. a premagnetization coil energized by a constantduration pulse and a control coil receiving the durationmodulated pulse in staggered relationship with the former.

United States Patent [1 1 Murtin et a1.

[5 1 ELECTRONIC CONTROL SYSTEM ron INTERNAL COMBUSTION ENGINE [75]Inventors: Fernand R. C. Murtin; Loic Mercier, both of Paris, France[73] Assignee: Socite' lndustrielle dElectronique et dlnformatique,Paris, France [22] Filed: Mar. 16, 1972 [21] Appl. No.: 235,289

Related U.S. Application Data [63] Continuation-impart of Ser. No.7,78], Feb. 2, 1970,

abandoned.

[30] Foreign Application Priority Data Jan. 31. 1969 France 69.02057Feb. 12.1969 France 69.03225 Mar. 7. 1969 France 69.06443 [52] U.S.C1...... 123/32 EA; 123/119 R; 123/32 AB [51] Int. Cl. F021) 3/00 [58]Field of Search 123/32 AB, 32 EA, 119 R [56] References Cited UNITEDSTATES PATENTS 3,456,628 7/1969 Bassot et a1. 123/32 EA 3,515,104 6/1970Reichardt 123/32 EA 3,522,794 8/1970 Reichardt et al.. 123/32 EA3.665398 5/1972 Kamazuka 123/32 EA 14 1 May 20, 1975 Du bno [57]ABSTRACT Fuel injectors for an internal-combustion engine are controlledby duration-modulated pulses whose width depends on a plurality ofparameters, namely the rotational speed and the temperature of theengine and the air pressure at two points of the intake manifold. Thewidth of the modulated pulses depends on the magnitude of one parameterand on binomials of the other parameters. A computer formed by cascadedoperational amplifiers with fractional gain and adding circuitsestablishes the variable operating period of the injectors which areprovided with two coils, i.e. a premagnetization coil energized by aconstant-duration pulse and a control coil receiving thedurationmodulated pulse in staggered relationship with the former.

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SHEET 5 OF 8 wmhwmw H QB r Wm ELECTRONIC CONTROL SYSTEM FOR INTERNALCOMBUSTION ENGINE This application is a continuation-in-part of ourcopending application Scr. No. 7,78l filed 2 February I970 and nowabandoned.

The present invention relates to a fuelinjectioncontrol system forinternal-combustion engines in which fuel is introduced under pressureat a point adjacent the intake ports of the piston cylinders of theengine with the aid of valves or injectors controlled by a generator ofpulses of variable duration. The width of the pulses Controlling theinjectors depends on sensed operating parameters or engine conditions;hence, a fuel-injection system can be considered as a computer designedfor driving from these parameters the signals controlling the circuitrywhich determines the duration of the injectiontiming pulses.

In the prior art, a variablc-durationpulse generator is usually arelaxation oscillator, namely aa monostable 2 element (monoflop) or abistable element (flip-flop) whose operating cycle is readily controlledby varying the resistance or capacitance of an R-C circuit or theinductance or resistance of an L-R circuit forming part thereof. U.S.Pat. No. 3.483.85Lfor example, discloses a flip-flop whose pulse periodis controlled by varying the mutual inductance of a transformer whereasUS. Pat. No. 3,456,628 describes a flip-flop whose pulse period iscontrolled by altering the value ofa variable resister.

The conventional fuelinjection systems take account of variousparameters. The most suitable parameter is the rate of air mass admittedto the cylinders but. as its value is quite difficult to obtain, it isgenerally replaced by the pressure and temperature ofthe air in theintake manifold. Other usual parameters are the speed of the engine andthe engine temperature.

According to our invention, injection is controlled by three parametersP, T, p. P is conventionally the back pressure in the intake manifoldahead of the cylinders; I its magnitude is generally proportional toload, varying inversely with the rotational engine speed for a giventhrottle opening. T is the engine temperature as measured in degreesKelvin. Parameter p is a subatmospheric pressure measured at aconstricted throat of the manifold in which is located theaccelerator-controlled throttle valve of the engine. The magnitude ofpdecreases with increasing air speed resulting from a narrowing of thegap around the throttle valve; parameter p is thus indicative of theposition of the accelerator pedal.

The three parameters P, T, p are related to the optimum injectioninterval 1' by the following equation:

PH+ NH +B H +7( n)l (I) wherein coefficient K, a, B, '7, T are constantsand N is the speed of the engine in turns per minute. Typical empiricalvalues for these constants are:

In the above equation, p and P are expressed in bars. The right side ofequation l) comprises a variable Kp which is multiplied by a product ofthree binomials.

The adjustable pulse generators of the prior art are not adapted toproduce pulses whose duration depends on the product of three binomials,each a function of a particular parameter; the duraction of their outputpulses is substantially determined by two parameters only. In amonotlop, for instance, the duration of the pulse depends on a productLC, of a resistance R times a capacitance C and the pulse period dependson a sum (R C, +R C R, and R being two resistances and C and C twocapacitances. Let us assume that a resistance R is allowed to varyproportionally to a binomial of a first parameter N according to R rt l(1N) and that a capacitance C is allowed to vary proportionally to abinomial of a second parameter P according C C( 1 BP then the pulseduration will vary according to RC=rc(l +aN) (l =BP) and the pulseperiod will vary according to R C +connected R C my (I a N l B P 2 2 22)( +B2 2) which, by neglecting the second-order terms. can betransformed into R C R C r c l+a,N,+,B,P,)+r c l+a N +B P l Thereforethe pulse duration varies proportionally to a product of two binomials.each depending on a single parameter, and the pulse period variesproportionally to a sum of two binomials, each depending on two parameters. For obtaining a pulse duration depending on three binomials,it would be necessary to let this pulse duration be substantiallydetermined by a combination of three variable impedance elements. Infact, we are aware only of teachings of pulse durations depending on twoparameters and on the logarithm of a third parameter (see Reference Datafor Radio Engineers," fourth edition, International Telephone andTelegraph Corporation, formulae on page 472). Obtaining athree-parameter-binomial dependence would require inclusion of anexponential function of the parameter which appears in the formula byits logarithm.

The injection system according to our invention includes a computerhaving circuit means for converting the critical parameter values intoanalog voltages; operational amplifiers are provided with suitablydimensioned feedback resistors to multiply these voltages with thecorresponding fractional constants a, B, 7, their outputs being thenadded to the original analog voltages with the aid of summing circuitsin order to form the desired binomials of the respective parameters.

Pursuant to a preferred feature of our invention, use is made ofhigh-speed electromagnetic injectors each provided with a pair ofsolenoid coils, i.e. a premagnetization or biasing coil and aninjection-control or working coil. Two pulses are respectively appliedto these coils, i.e. a priming pulse of constant duration and a controlpulse whose width depends on the measured parameters. The primary pulsebegins before the control pulse and terminates after the latter has comeinto existence.

The above and other features of our invention will be describedhereinafter in detail with reference to the accompanying drawing inwhich:

FIG. 1 represents in the form of a block diagram an injection-controlsystem for a vehicular internalcombustion engine according to ourinvention;

FIG. 2 is a perspective view of the engine with the injectors andassociated circuitry;

FIG. 3 is a somewhat diagrammatic view of a part of a gasoline engineprovided with the injection-control system of FIG. 1;

FIG. 4 is a cross-sectional view of a pressure sensor included in thesystem;

FIG. 5 is a cross-sectional view of a fuel injector also included in thesystem;

FIG. 6 is a circuit diagram of a sensor-controlled voltage generatorshown in H6. 1;

FIG. 7 is a circuit diagram of a pulse-duration modulator also shown inFIG. 1;

FIG. 8 is a set of graphs showing the signal waveforms at differentpoints of the circuit of FIG. 7; and

FIG. 9 schematically represents a monitor circuit included in thesystem.

In FIGS. 1 and 2 we have diagrammatically illustrated an automotivegasoline engine 1, a temperature sensor 2 and two pressure sensors orgauges 3 and 3'. The engine (FIG. 2) comprises a driven shaft 11, anintake manifold l2-and four cylinders 13a, 13b, 13c, 13d. Shaft ll, likethe cam shaft of conventional four-stroke engines, rotates at half thespeed of the engine crankshaft (not shown) acted upon by the cylinderpistons. Four electromagnetic pick up coils 14a, 14b, 14c, 14d areequispaced about the shaft 11 for periodic excitation by a permanenttrigger magnet 15 revolving on the shaft. Synchronizing pulses, markingthe beginning of respective injection cycles for the several cylinders,are produced in the coils when the magnet passes in front thereof andare fed, through respective leads 10a, 10b, 10c, 10d, on the one hand toa pulse-duration modulator 6 and on the other hand to the setting or linputs of respective injector-control flip-flops 7a, 7b, 7c, 7 d.

Four output terminals of modulator 6 are connected, through leads 60a60d, to resetting or 0" inputs of the flip-flops 7a 7d.

The output terminals of temperature and pressure sensors 2, 3 and 3' areconnected via respective leads 20, 30, 30' to a jointly controlledanalog-voltage generator 5.

Flip-flops or bistables are electronic switches well known in theelectronics art and are described, for example in a textbook by JacobMillman and Herbert Taub, McGraw-Hill Book Company, Inc., NY. l956,chapter 5, pages 140 ff and FIG. 5.2. A flip-flop is essentially atwo-transistor regenerative circuit that can exist indefinitely ineither of two stable states (which may be designated 0 and l and can becaused to make an abrupt transition from one state to the other. It isused for the generation of rectangular waves from short pulses and forstoring single or multiple bits in binary registers or pulse counters.The trigger pulse employed to induce a transition from one state to theother may be introduced in such a manner as to produce eithersymmetrical or unsymmetrical triggering. ln unsymmetrical triggering, atrigger pulse applied to one input is effective in inducing a transitionin only one direction (generally termed setting"). A second triggerpulse from a separate source must be applied to a different input toachieve the reverse transition (resetting). [n symmetrical triggering,successive trigger pulses a plied to a common input switch the flip-flopto its alternate state from whichever state it happens to be in. The twooutputs ofa flip-flop energized in the l and 0 states will be calledhereinafter the set and reset outputs, respectively.

As distinct from flip-flops, monoflops have a normal or 0 state fromwhich they may be switched to an offnormal or 1 state for apredetermined period, as determined by a built-in time-constant network.They may, therefore, be used as timing means to measure relatively shortintervals.

The set outputs of flip-flops 7a, 7b, 7c, 7d actuate, by way ofrespective leads a, 70b, 70c, 70d and AND gates 9a, 9b, 9c, 9d,associated solenoid valves 18a, 18b, 18c, 18d located at the fuel inletsof cylinders 13a, 13b, 13c, 13d near the upper-dead-center positions oftheir pistons.

AND gates are disclosed on pages 397-400 of the textbook above referredto. An AND gate has two or more inputs to each of which is applied apulse of common polarity. The gate has a single output at which a pulseappears if and only if pulses are applied simultaneously to all inputs.If the input pulses are not of the same duration, the output pulse willbe present only as long as the input pulses overlap.

The other inputs of AND gates 90 9d are normally energized throughconductors 400C and 40bd by a monitor circuit 4 responsive to theposition of an accelera tor pedal 41 aboard the vehicle and to theengine speed as defined by the frequency of the pulses on lead 100.

The reset outputs of flip-flops 70, 7c, on the one hand, and 7b, 7d, onthe other hand, are connected to the inputs of AND gates Sac and Sbdwhose outputs are returned to modulator 6 through leads 8011c and bd,respectively.

Under conditions of small or negative loads, e.g. during downhilldriving, monitor circuit 4 responds to the combination of retractedpedal and relatively high velocity to de-energize the conductors 4000and 40bd, thereby closing AND gates 9a 9d and inhibiting the operationof the injection actuators 18a l8d regardless of the states of theassociated flip-flops 7a 7d. This inhibition of combustion allows theengine to operate as a more effective brake and further reduces thepollution of the atmosphere. Circuitry suitable for use in component 4will be described below with reference to FIG. 9.

Temperature sensor 2 (H6. 3) is a temperaturedependent resistor locatedin cylinder 13a. Such resistors, giving an output signal proportional(with a proportionality factor 7) to the difference between an actualtemperature T and a reference temperature T are known in theheat-control art. For example, resistors with 'y 5.10 and T 333K areavailable on the market under the commercial name TUS 23".

Pressure sensor 3 (also representative of sensor 3') has beenillustrated in H0. 4. This sensor comprises a metallic housingconsisting of two parts 301, 302 which are bolted or otherwise securedto each other by means not shown and between which a resilient,preferably metallic, diaphragm 303 is clamped. The interior ofhousing'30l, 302 is divided by this diaphragm into two compartments 304,305, compartment 304 communicating via a bore 306 in a threaded nipple307 with the air space (specifically the manifold 101 of H6. 3 describedhereinafter) whose pressure is to be measured; an orifice 308 connectsthe compartment 305 with a source of substantially constant fluidpressure, advanta geously the outer atmosphere. Diaphragm 303 supports ametallic boss 309 from which a conducting rod 310 slidably projectsthrough a dielectric sleeve 31] in housing portion 302; rod 310 issurrounded with sliding fit by a metallic bushing 312 connected to itsoutgoing terminal lead 30. A spur 314 on rod 310 contacts a coil ofresistance wire 315 wound around an insulating core 316; wire 315 isgrounded at one end of housing portion 302 and connected at its otherend to a positive bus bar 61. Thus, elements 314 and 315 constitute apotentiometer delivering on conductor 30 a voltage which, through asuitable design of resistance coil 315, may be caused to varysubstantially linearly with the pressure differential acting upon thediaphragm 303.

FIG. 5 shows a preferred construction of an injector 18 representativeof any of the fuel injectors 18a 180' shown in F10. 2. A cylindricalhousing 1,801 of nonmagnetic material threadedly engages a nozzle 1,802whose outlet 1,803 is normally closed by a beveled tip 1804 of a tubulararmature 1805 of magnetically permeable material which is slidablyguided in a similarly permeable ring 1807. Another tubular member 1808of permeable material, confronting the armature 1805 across an air gap1809, is fixedly clamped within housing 1801 through the intermediary ofring 1807, a tubular'winding support 1810 enclosing the members 1805 and1808, a ferromagnetic shell 1811 embracing the ring 1807 and the support1810, and an internally threaded insert 1812 projecting from the housingend opposite nozzle 1802. A nipple 1813 is screwed into insert 1812 andforms an abutment for a compression spring 1814 received within members1805 and 1808, this spring tending to urge the tip 1804 against its seat1803. A fluid path for fuel entering the bore of nipple 1813 extendsthrough the spring chamber within members 1805 and 1808 and through apair of lateral orifices 1815 in tip 1804 to a space 1816 surroundingthat tip, this space being open toward the outside upon a withdrawal oftip 1804 from nozzle mouth 1803.

A magnetic circuit, interrupted by the air gap 1809, will thus be seento include the permeable elements 1805, 1807, 1808 and 1811, thiscircuit being formed around a pair of annular clearances which receivetwo electromagnetic coils 1817, 1818 carried on support 1810. Asdescribed hereinafter with reference to FIG. 1, windings 1817 and 1818are sequentially energized in staggered relationship and are aidinglyintercon nected so that their joint excitation opens the injection valverepresented by armature tip 1804 and nozzle mouth 1803. The preliminaryenergization of biasing winding 1817, insufficient in itself to displacethe armature 1805 against the force of spring 1814, generates enoughflux to shift the operating point of the electromagnetic circuit to thelinear portion of its hysteresis curve whereby the valve opens promptlyupon the subsequent energization of the working winding 1818. To-

ward the end of the injection interval, biasing winding 1817 isde-energized (preferably after having been energized for a fixed period)but the remanence of the ferromagnetic elements, together with thecontinuing current flow in winding 1818, holds the armature 1805retracted while again established an operating point on the linearportion of the hysteresis curve. Upon the deenergization of winding1818, after a variable period depending upon the controlling parameters,spring 1814 quickly returns the armature to its closure position.

We shall now refer to FIG. 3 wherein elements already shown in FIGS. 1and 2 include the monitor circuit 4, the pedal 41, the control shaft 11with its magnet 15 and the electromagnetic pick-up coil 14a excitablethereby, together with the output lead of that coil extending topulse-duration modulator 6. The tempe rature and pressure sensors 2, 3and 3' are connected to analog-voltage generator 5 via respectiveconductors 20, 30 and 30'. Pressure sensors 3 and 3' are mounted in thewall 102 of an intake manifold 101 communicating with the atmospherethrough a port 103 from which it is separated by a constriction 104. Abutterfly-type throttle valve or damper 105, rotatable about a gudgeon106, is mechanically linked with the pedal 41 for clockwise rotationwhen the pedal is depressed against the force of a restoring spring 107.Pedal 41 is electri cally grounded through its contact with the metallicmanifold housing 102 which has a further constriction 108 separating themanifold 10] from a neck 109 leading to a combustion cylinder partlyshown in 13a. This cylinder has an inlet port 111 closable by a poppetvalve 112 which is conventionally biased into a closure position by aspring 113 and is periodically opened by a cam shaft which may form anextension of shaft 11. Temperature sensor 2 is disposed in a coolingchannel 114 within the wall of cylinder 130 through which water cooledby the radiator of the engine is circulated. in the case of anair-cooled engine, this temperature sensor 2 may be mounted in directcontact with the cylinder wall. It will be understood that the remainingcylinders have similar inlets branched off the manifold 101 via otherconstrictions such as that shown at 108.

Fuel injector 18a is conncted via a supply conduit 115 to thehigh-pressure side of an electrical gear pump 116 which delivers thefuel at constant pressure, independent of the engine speed. Thelow-pressure side of the pump communicates with a fuel reservoir 117.injector 18a is controlled from flip-flop 7a through AND gate 9a via alead 90a (see also FIG. 1).

With the throttle valve in a position of near closure, corresponding toidling of the engine under noload conditions, pedal 41 comes to restagainst an adjustable backstop in the form of a screw 118 seated in aninsulating bushing 119 on housing 102. A conductor 400, leading fromscrew 118 to monitor 4, is therefore grounded whenever pedal 41 is inits retracted position.

Pressure sensor 3 communicates with a bore 121 which opens into themanifold 101 at the narrowest point of its constricted throat 104 todetect the subatmospheric pressure p existing at this point whenevercombustion air streams inwardly past the damper 105 toward thecylinders, the absolute magnitude of this pressure varying inverselywith air speed. Pressure sensor 3 communicates with a similar bore 122,opening directly into the manifold downstream of bore 121 betweenconstrictions 104 and 108, to measure a back pressure P proportional tothe load as explained above.

FIG. 6 shows the details of the sensor-controlled analog-voltagegenerator 5 of FIGS. 1 and 2.

The arm of the potentiometer 315 of pressure sensor 3 is connected tothe direct or noninverting input 30 of an operational amplifier 501having a voltage divider 502-503 connected between its output andground. The junction of resistors 502 and 503 is connected to theinverting input of amplifier 501. The gain of the amplifier is (RmRsosllR (see IEEE Spectrum," Apr. 1971, Linear Circuit Applications ofOperational Amplifiers" by Larry L. Schick, P16. 298, page 48) which ismade equal to constant K of equation 1 The output signal of amplifier501 is thus the analog of the product Kp.

The signal Kp issuing from operational amplifier 501 is applied to thepotentiometer of sensor 3'. The arm of this potentiometer is connectedto the direct or noninverting input 30' of an operational amplifier S04having a voltage divider 505-506 connected between its output andground. The junction of resistors 505 and 506 is connected to theinverting input of an amplifier 504 whose gain is (R R )/R which is madeequal to constant B. The output signal of amplifier 504 is thus theanalog of Kp X BP. The output signals of amplifiers 501 and 504 areapplied to a network of identi cal summing resistors 507, 508, S09forming an adding network (see Reference Data for Radio Engineers,"fourth edition, International Telephone and Telegraph Corporation, page458). Resistor 509 has an extremity grounded and its other extremityconnected to the direct or noninverting input of an operationalamplifier 510. The signal voltage vsng at this input can be expressed byOperational amplifier 510 is connected as a voltage to-current converter(see IEEE Spectrum already cited, FIG. 26, page 47). The arrangementcomprises an input series resistor 511, a feedback resistor 512connected to the inverting output, a voltage divider 513-514 connectedbetween the amplifier output and ground, and the temperature-dependentresistor element 2 of thermal coefficient 31 connected between thedirect input and ground in parallel with resistor 514. The resistance Rof this temperature sensor has a value 'y(TT,,). The junction ofresistors 513 and 514 is also connected to the direct input. It is known(eg. from the cited reference) that if ats/ 514 am 511 the current i:through resistor 2 is proportional to the input signal Kp( l-l-BP) inaccordance with the relation ship Therefore, the signal voltage V;across resistor 2 is given by The signal voltages V and V; are added ina summing network formed by identical resistors 517, 518, 5l9, similarto the summing resistors 507, 508, 509. The signal voltage V acrossresistor 519 is therefore expressed as follows:

The ungrounded terminal of resistor 519 is connected to two parallelpaths, the first comprising a re sistor 520 and the second being formedfrom three series resistors 521, 522, 523, these two paths beinggrounded through a parallel resistor 524.

The train of pulses from coil 14a (FIG. 3), whose repetition frequencyor cadence is proportional to engine speed N, is applied through lead ato the gate of a field-effect transistor 516. The source of transistor516 is grounded and its drain is connected to an integrating R-C circuitformed of a series resistor 522 and a shunt capacitor 525. Resistor 521is a decoupling resistor and resistors 520, 523, 524 are identicalelements of a summing network. The signal voltage developed acrossresistor 520 is the voltage V of equation (3); the com- 8 posite signalvoltage V appearing across resistor 523 is given by 523 IINKM l+B )l o)lwherein a is determined by the relative magnitude of impedances 521,522, 525. The final analog voltage V appearing across shunt resistor 524is proportional pt 1+ 1N l+/ )l i+-/( .)1 and consequently to thedesired injection interval 1- as per equation (1).

Anolog voltage V is normally applied to a buffer operational amplifier526 whose output signal controls the pulse-duration modulator 6 througha lead 56.

In FIG. 7 we have shown modulator 6 as including a power supply such asthe battery of the vehicle driven by the engine. Battery 60 has itspositive terminal connected to the aforementioned bus bar 61 maintainedat, say, +6 volts, its negative terminal being connected to a bus bar 62carrying, say 6 volts whereas an intermediate point is connected to agrounded bus bar 63. The bus bars 61, 62, 63 serve to feed and bias ananalog-voltage repeater 64, a sawtooth-voltage generator 65, acomparator 66 comparing the voltages respectively produced by circuits64 and 65, and a starting circuit 67.

The analog-voltage repeater 64 is a Wheatstone bridge having fourcorners I, ll, III, IV and four arms. The first arm l-ll is formed bythe analog-voltage generator S of FIG. 6. The second arm ll-lll nd thethird arm lll-lV are formed by respective resistors 641 and 642, thelatter being in parallel with a capacitor 643. The fourth arm lV-l isformed by two resistors 644 and 645, a transistor 640 bridging theresistors 642 and 644. Transistor 640 has its emitter grounded throughbus bar 63 and its collector connected to positive bus bar 61 through aresistor 645. The base of transistor 640 is biased through a variableresistor 646 and connected to the starting circuit 67.

The corners l and ll] of the supply diagonal of the Wheatstone bridgeare respectively connected to bus bars 61 and 63 whereas the corners lland IV of the reading diagonal of the bridge are respectively connectedto the direct and inverting input terminals of an operational amplifier647. The output 647' of operational amplifier 647 is connected to aninput 667' of comparator 66. Operating current is supplied to amplifier647 by means of leads 649 and 649', respectively connected to bus bars61 and 62.

A pair of oppositely poled Zener diodes 648 and 648' are connectedacross the reading diagonal ll-lV of the bridge in order to limit themagnitude of input signal of either polarity fed to amplifier 647.

The function of transistor 640 and capacitor 643 will be explained withthe operation of the pulse-duration modulator 6.

i The sawtooth-voltage generator 65 comprises a PNP transistor 650having a capacitor 651 in its collector circuit and a resistor 652 inits emitter circuit. The base of transistor 650 is biased by a voltagedivider formed from two resistors 653 and 654, resistor 654 beingshunted by a capacitor 655. Capacitor 651 is bridged by an NPNtransistor 656 serving for its discharge as described hereinafter. lt iswell known (see the textbook above referred to, page 236) that thesignal developed across the capacitor 651 has a sawtooth waveform. Thesignal available at output terminal 657 of sawtooth-voltage generator 65is applied to the other input terminal 667 of comparator 66.

Signal comparator 66 comprises two mirrorsymmetrical NPN transistors 660and 660 having a common emitter circuit in which an injector transistor66] and a resistor 662 are serially connected to negative bus bar 62;the paired transistors 660 and 660' are provided with respectivecollector resistors 663 and 663. Transistors 660, 660' and 661 form adifferential amplifier; transistor 66] acts as a source of current whichdivides between transistors 660 and 660' according to the base biasthereof.

The collector of NPN transistor 660 is further connected to the base ofa PNP transistor 664 having an emitter directly tied to bus bar 61 and acollector connected to ground on bus bar 63 through two series resistors664' and 664". The junction of resistors 664' and 664" is connected tothe base of an NPN transistor 665 having its collector connected to busbar 61 through a resistor 665' and its emitter directly connected togrounded bus bar 63. Resistors 661' and 661" form a voltage dividerbetween ground and negative battery for biasing the base ofcurrent-injecting transistor 66].

The collector of transistor 665 is connected to the output terminal 668of comparator 66 through a circuit formed by a series capacitor 669' anda shunt resistor 669". Output terminal 668 is tied to the resettinginputs of flip-flops 7a and 7c.

The starting circuit 67 comprises two PNP transistors 670 and 670 havingemitter resistors 671, 671 and collector resistors 672, 672'. Thecollectors of transis' tors 670 and 670 are respectively connected tothe bases of transistors 656 and 640, their bases being jointlyconnected to the output of NAND gate Sac.

Generally, the pulse-duration modulator shown in FIG. 7 operates asfollows (see also FIG. 8):

Flip-flops 7a and 7c are alternately operated in phase opposition bytrigger pulses 910a, 9100 on leads 10a, 10c respectively. Leads 700, 70capply durationmodulated pulses 970a, 970C of width 7 to thefuelinjection valves 180, 186 (FIG. 2) unless this action is inhibitedas later described. The injection interval is terminated whenever thecharge of capacitor 651 of sawtooth-voltage generator 65 reaches thelevel of the voltage generated by the analog-voltage repeater 64.

When the rising amplitude of the voltage on input 667 matches that ofthe signal on input 667', transistor 660 conducts whereby the base oftransistor 664 is driven negative to turn the latter transistor on.Thereupon the transistor 665 becomes conductive and develops a negativespike 9600c across resistor 665', this spike being applied through acoupling capacitor 669' to the resetting inputs of flip-flops 7a and 7cto reverse whichever these flip-flops had previously been set by a pulse9100 or 9101 on lead 100 or 10c, respectively.

NAND gate Sac is connected to the reset outputs of flip-flops 7a and 7cand gives rise to pulses 980m which persist as long as flip-flops 7a and7c are simultaneously reset. Pulses 980m are applied through lead 80acto the joined bases of two mirror-symmetrical PNP transistors 670 and670' which thus become conductive. The resulting pulses developed acrosstheir collector resistances 672 and 672 respectively turn on thetransistor 656 ofsawtooth-voltage generator 65 and the transistor 640 ofvoltage repeater 64. Capacitor 651 is thereby discharged throughtransistor 656; upon the termination of each pulse 980ac, capacitor 651begins to charge along a line V (representing the voltage on terminal667) to the level of variable voltage V on terminal 667'.

Resistor 642 and capacitor 643 form an integrating circuit for biasingthe transistor 640. The effect of pulses 980ac as amplified bytransistor 670' is to build up a bias voltage across capacitor 643,thereby reducing the effective magnitude of the analog voltage V appliedvia lead 56 to the noninverting input of operational amplifier 647whereby the output voltage V of this amplifier depends upon the balancebetween the voltage V and the reference voltage V applied to itsinverting input.

The higher the positive output signal V of operational amplifier 647,the longer will be the time required for condenser 651 to charge up tothe level of that signal. This lengthens the injection interval 7 (line700, FIG. 8) and correspondingly shortens the complementary period 1"for the discharge of condenser 651. As a result, reference voltage Vgoes more positive whereby the effective input signal of amplifier 647in creases more slowly. as does the base potential oftransistor 660',with consequent limitation of the lengthening of the injection interval.Thus, the feedback from the flip-flops 7a, 7c via conductor 8011c to theinput of amplifier 647 stabilizes the injection interval 'r.

Such a lengthening of the injection interval, due to a more positivedriving voltage V from sensing circuit 5, indicates a change inoperating conditions of a nature calling for additional fuel. ln theopposite case, of course, the voltage at the direct input of 647 will decrease to foreshorten the injection time.

FlG. 9 represents in detail the monitor circuit 4 of FIG. 1. Itcomprises an integrating R-C network formed of a resistor 401 and acapacitor 402, resistor 401 being connected to lead 100. Network 401-402is similar to the integrating network 522-525 of FIG. 6 in that thecharge voltage across its capacitor 402 depends on the frequency ofpulses 910a, i.e. on the speed of the engine. The voltage of capacitor402 is compared in an operational amplifier 403 with a predeterminedreference voltage obtained from a voltage divider 404-405. The outputvoltage of amplifier 403 is positive when the capacitor potentialexceeds the reference voltage and is zero when the capacitor potentialis lower than the reference voltage.

The output lead 406 of amplifier 403 is connected to an inverting inputof an AND gate 407 and in parallel therewith to a noninverting input ofa NAND gate 412. Lead 400 groundable by pedal 41 (cf. FIG. 3) isconnected in parallel to the other, inverting inputs of AND gate 407 andNAND gate 412; this lead is connected to positive potential on bus bar61 through a resistor 414. The output of AND gate 407 is connected to anelectromagnetic relay 408 (FIG. 6) through a lead 409 whereby the outputof NAND gate 412 is connected to lead 4000 (FIG. 1). With relay 408unoperated, its armature 4081 connects the resistance network 520-523 tothe operational amplifier 526 feeding the output lead 56.

If the pedal 41 is retracted to its idling position and, at the sametime, the engine speed is relatively low, there is ground potential online 400 and zero voltage on line 406. Under these conditions, AND gate407 opens and energizes relay 408 (FIG. 6) whose armature 4081 thereupondisconnects the analog voltage of generator from the input of amplifierS26 and connects thereto in its stead a constant reference potentialobtained from a voltage divider 410-411. NAND gate 412 conducts andenergizes its output lead 40ac so that coincidence gates 9a and 9c(FIG. 1) are enabled to pass the timing pulses 970a and 9706' on leads70a and 70c, respectively, whose duration at this point is fixed at aminimum consistent with the power requirements at low load.

If, with the pedal 41 still retracted, the engine 1 accelerates beyondthe speed threshold established by voltage divider 404, 405, gate 407 isblocked so that relay 408 releases and restores the connection betweenvoltage generator 5 and pulse-width modulator 6. NAND gate 412 is nowcut off and gates 90, 9c are blocked, thereby preventing injection toavoid waste of fuel, reduce atmospheric pollution and help slow down theengine.

When pedal 41 is depressed to indicate a demand for power, lead 400 goespositive so that AND gate 407 remains inhibited whereas NAND gate 412energizes its output lead 40ac irrespectively of the state ofconductivity of amplifier 403. This situation, occurring during normaldriving, brings into play the multiple-parameter injection controldescribed above.

Whenever AND gates 9a 9d are enabled by the energization of their inputleads 4000 and 40bd from men itor 4, the injection control pulses 970a970d (FIG. 8) respectively passing therethrough from conductors 70a 70dappear on their output leads 90a 90d (generally indicated at 90 in FIG.5) as actuating pulses which energize the second-stage solenoid coils orworking windings 1818 of the corresponding injectors 18a 18d. Theassociated first-stage solenoid coils or biasing windings 1817 thereofare energized, in staggered relationship with windings 1818, by pulses1,490a 1,490d of constant width (illustrated in dot-dash lines in FIG.5) by corresponding monoflops 413a 413d; these monoflops are tripped bythe synchronizing pulses 910a 910d from coils 14a 14d transmitted to themonoflops via leads a 10d. Delay networks 91a 91d in leads 90a 90d serveto offset the leading edges of control pulses 970a 970d from those ofpriming pulses 1490a l490d with which they are seen to coincide in FIG.8, thereby making the injection interval r definitely coincident withthe respective control pulse. The delay introduced by networks 910 91dshould be sufficient to let the trailing edges of the shortest controlpulses 970a 970d lag behind those of the associated priming pulses 1490a149041.

The pulses 97012 and 970d, shown in FIG. 8, are generated by flip-flops717, 7d or FIG. 1 under the control of setting pulses from leads 10b,10d and resetting pulses from leads 60!), 6011, the latter beingperiodically energized by a section of pulse-width modulator 6 (notillustrated in detail) identical with the one shown in FIG. 7 forfeeding the resetting leads 60a, 60c of flipflops 70, 7c.

Modulator 6 may be regarded, in part, as an analog/- digital converterwhich derives from the parametercontrolled analog output of computer 5 aset of binary signals adapted to be used in the logic circuitry 70 7detc. of FIG. 1.

We claim:

1. A fuel-injection-control system for an internalcombustion enginehaving a plurality of piston cylinders provided with intakes forcombustion air, respective fuel injectors feeding said cylinders, and ashaft driven by the thrust of an exploding air-fuel mixture ignited ineach cylinder, comprising:

electric actuating means for each of said fuel injectors;

a generator of synchronizing pulses having a cadence proportional toengine speed;

electric sensing means in said engine responsive to differentcombustion-determining parameters, said sensing means including a firstpressure gauge positioned at a constriction of a common intake manifoldfor said cylinders, a second pressure gauge positioned at a location insaid manifold downstream of said constriction, and atemperature-responsive resistor in close proximity to at least one ofsaid cylinders;

voltage-generating means connected to said generator and to said sensingmeans for synthesizing from their outputs an analog voltage as afunction of said parameters and said engine speed; and

timing means controlled by said voltage-generating means for energizingsaid actuating means for a recurrent period proportional to said analogvoltage, said timing means including an analog/digital converter andelectronic switch means responsive to binary output signals from saidconverter, said switch means being connected to said generator forestablishing recurrent operating cycles for said injectors under thecontrol of said synchronizing pulses;

said voltage-generating means comprising a first operational amplifierhaving an input circuit including said first pressure gauge, a secondoperational amplifier in cascade with said first amplifier having aninput circuit including said second pressure gauge, and a thirdoperational amplifier in cascade with said second amplifier having aninput circuit including said temperature-responsive resistor.

2. A system as defined in claim 1, further comprising first summingmeans in the input circuit of said third amplifier for adding the outputof said first amplifier to that of said second amplifier, second summingmeans for adding the outputs of said first, second and third amplifiersto generate a composite signal voltage, and integrating means connectedto said second summing means and to said generator for multiplying saidsignal voltage by a speed factor dependent upon the cadence of saidsynchronizing pulses.

3. A system as defined in claim 1 wherein said composite signal voltageis proportional to the product of a first parameter times a binomial ofa second parameter multiplied by a binomial of the third parameter,further comprising third summing means connected to said second summingmeans and said integrating means for introducing a binomial of enginespeed into said analog voltage as said speed factor.

4. A system as defined in claim 2 wherein at least said second and thirdamplifiers have fractional gains.

5. A system as defined in claim 4 wherein said analog voltage isproportional to an injection period 1' Kp(l+aN) (1+3?) [l+*y(T'-Tu)l. Nbeing the engine speed, 11 being the air pressure at said constriction,P being the air pressure at said downstream location, K being aconstant, B being the gain of said second amplifier, being the thermalcoefficient of said temperature-responsive resistor, 01 being a functionof impedance values of said integrating means.

6. A fuel-injection-control system for an internalcombustion enginehaving a plurality of piston cylinders provided with intakes forcombustion air, respective fuel injectors feeding said cylinders, and ashaft driven by the thrust of an exploding air-fuel mixture ignited ineach cylinder, comprising:

electric actuating means for each of said fuel injectors;

a generator of synchronizing pulses having a cadence proportional toengine speed.

a first, a second and a third sensor in said engine responsive todifferent combustion-determining parameters;

voltage-generating means connected to said generator and to said sensingmeans for synthesizing from their outputs an analog voltage as afunction of said parameters and said engine speed; and

timing means controlled by said voltage-generating means for energizingsaid actuating means for a recurrent period proportional to said analogvoltage, said timing means including an analog/digital converter andelectronic switch means responsive to binary output signals from saidconverter, said switch means being connected to said generator forestablishing recurrent operating cycles for said injectors under thecontrol of said synchronizing pulses;

said voltage-generating means comprising a first operational amplifierhaving an input circuit including said first sensor, a secondoperational amplifier in cascade with said first amplifier having aninput circuit including said second sensor, and a third operationalamplifier in cascade with said second amplifier having an input circuitincluding said third sensor.

7. A system as defined in claim 6, further comprising first summingmeans in the input circuit of said third amplifier for adding the outputof said first amplifier to that of said second amplifier, second summingmeans for adding the outputs of said first, second and third amplifiersto generate a composite signal voltage, and integrating means connectedto said second summing means and to said generator for multiplying saidsignal voltage by a speed factor dependent upon the cadence of saidsynchronizing pulses.

8. A system as defined in claim 6 wherein the admission of combustionair to said cylinders is controlled by an accelerator pedal adapted tobe depressed from a retracted position to indicate a demand forincreased engine power, further comprising monitoring means connected tosaid switch means and responsive to the position of said pedal forinhibiting the energization of said actuating means under the control ofsaid analog voltage in a state of reduced engine load.

9. A system as defined in claim 8 wherein said monitoring means isconnected to said generator and is ef fective in said retracted positionof the pedal to establish a predetermined energization period for saidactuating means at relatively low engine speeds and permanentlyde-energizing said actuating means at relatively high engine speeds.

10. A system as defined in claim 9 wherein said timing means includes asource of constant voltage connectable by said monitoring means to saidconverter, in lieu of said analog voltage, at said relatively low enginespeeds in said retracted pedal position.

1]. A system as defined in claim 6 wherein said actuating meanscomprises for each injector a pair of aidingly connected solenoid coilsincluding a biasing coil and a working coil, said switch means beingresponsive to said synchronizing pulses for supplying a priming pulse orfixed duration to said biasing coil at the beginning of an operatingcycle and for subsequently supplying a timing pulse of variable width,proportional to said analog voltage, to said working coil in staggeredrelationship with said priming pulse, said timing pulse being effectiveonly in the presence of said priming pulse to actuate the injector andmaintaining same actuated past the termination of said priming pulse.

1!: k i l

1. A fuel-injection-control system for an internal-combustion enginehaving a plurality of piston cylinders provided with intakes forcombustion air, respective fuel injectors feeding said cylinders, and ashaft driven by the thrust of an exploding air-fuel mixture ignited ineach cylinder, comprising: electric actuating means for each of saidfuel injectors; a generator of synchronizing pulses having a cadenceproportional to engine speed; electric sensing means in said engineresponsive to different combustion-determining parameters, said sensingmeans including a first pressure gauge positioned at a constriction of acommon intake manifold for said cylinders, a second pressure gaugepositioned at a location in said manifold downstream of saidconstriction, and a temperature-responsive resistor in close proximityto at least one of said cylinders; voltage-generating means connected tosaid generator and to said sensing means for synthesizing from theiroutputs an analog voltage as a function of said parameters and saidengine speed; and timing means controlled by said voltage-generatingmeans for energizing said actuating means for a recurrent periodproportional to said analog voltage, said timing means including ananalog/digital converter and electronic switch means responsive tobinary output signals from said converter, said switch means beingconnected to said generator for establishing recurrent operating cyclesfor said injectors under the control of said synchronizing pulses; saidvoltage-generating means comprising a first operational amplifier havingan input circuit including said first pressure gauge, a secondoperational amplifier in cascade with said first amplifier having aninput circuit including said second pressure gauge, and a thirdoperational amplifier in cascade with said second amplifier having aninput circuit including said temperature-responsive resistor.
 2. Asystem as defined in claim 1, further comprising first summing means inthe input circuit of said third amplifier for adding the output of saidfirst amplifier to that of said second amplifier, second summing meansfor adding the outputs of said first, second and third amplifiers togenerate a composite signal voltage, and integrating means connected tosaid second summing means and to said generator for multiplying saidsignal voltage by a speed factor dependent upon the cadence of saidsynchronizing pulses.
 3. A system as defined in claim 1 wherein saidcomposite signal voltage is proportional to the product of a firstparameter times a binomial of a second parameter multiplied by abinomial of the third parameter, further comprising third summing meansconnected to said second summing means and said integrating means forintroducing a binomial of engine speed into said analog voltage as saidspeed factor.
 4. A system as defined in claim 2 wherein at least saidsecond and third amplifiers have fractional gains.
 5. A system asdefined in claim 4 wherein said analog voltage is proportional to aninjection period Tau Kp(1+ Alpha N) (1+ Beta P) (1+ gamma (T-To)), Nbeing the engine speed, p being the air pressure at said constriction, Pbeing the air pressure at said downstream location, K being a constant,Beta being the gain of said second amplifier, gamma being the thermalcoefficient of said temperature-responsive resistor, Alpha being afunction of impedance values of said integrating means.
 6. Afuel-injection-control system for an internal-combustion engine having aplurality of piston cylinders provided with intakes for combustion air,respective fuel injectors feeding said cylinders, and a shaft driven bythe thrust of an exploding air-fuel mixture ignited in each cylinder,comprising: electric actuating means for each of said fuel injectors; agenerator of synchronizing pulses having a cadence proportional toengine speed; a first, a second and a third sensor in said engineresponsive to different combustion-determining parameters;voltage-generating means connected to said generator and to said sensingmeans for synthesizing from their outputs an analog voltage as afunction of said parameters and said engine speed; and timing meanscontrolled by said voltage-generating means for energizing saidactuating means for a recurrent period proportional to said analogvoltage, said timing means including an analog/digital converter andelectronic switch means responsive to binary output signals from saidconverter, said switch means being connected to said generator forestablishing recurrent operating cycles for said injectors under thecontrol of said synchronizing pulses; said voltage-generating meanscomprising a first operational amplifier having an input circuitincluding said first sensor, a second operational amplifier in cascadewith said first amplifier having an input circuit including said secondsensor, and a third operational amplifier in cascade with said secondamplifier having an input circuit including said third sensor.
 7. Asystem as defined in claim 6, further comprising first summing means inthe input circuit of said third amplifier for adding the output of saidfirst amplifier to that of said second amplifier, second summing meansfor adding the outputs of said first, second and third amplifiers togenerate a composite signal voltage, and integrating means connected tosaid second summing means and to said generator for multiplying saidsignal voltage by a speed factor dependent upon the cadence of saidsynchronizing pulses.
 8. A system as defined in claim 6 wherein theadmission of combustion air to said cylinders is controlled by anaccelerator pedal adapted to be depressed from a retracted position toindicate a demand for increased engine power, further comprisingmonitoring means connected to said switch means and responsive to theposition of said pedal for inhibiting the energization of said actuatingmeans under the control of said analog voltage in a state of reducedengine load.
 9. A system as defined in claim 8 wherein said monitoringmeans is connected to said generator and is effective in said retractedposition of the pedal to establish a predetermined energization periodfor said actuating means at relativeLy low engine speeds and permanentlyde-energizing said actuating means at relatively high engine speeds. 10.A system as defined in claim 9 wherein said timing means includes asource of constant voltage connectable by said monitoring means to saidconverter, in lieu of said analog voltage, at said relatively low enginespeeds in said retracted pedal position.
 11. A system as defined inclaim 6 wherein said actuating means comprises for each injector a pairof aidingly connected solenoid coils including a biasing coil and aworking coil, said switch means being responsive to said synchronizingpulses for supplying a priming pulse or fixed duration to said biasingcoil at the beginning of an operating cycle and for subsequentlysupplying a timing pulse of variable width, proportional to said analogvoltage, to said working coil in staggered relationship with saidpriming pulse, said timing pulse being effective only in the presence ofsaid priming pulse to actuate the injector and maintaining same actuatedpast the termination of said priming pulse.